Evolution Skulls of a long-tailed weasel (top), a stoat (bottom left) and least weasel (bottom right), as illustrated in Merriam's Synopsis of the Weasels of North America

The long-tailed weasel is the product of a process begun 5"?7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents. The long-tailed weasel's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The long-tailed weasel arose in North America 2 million years ago, shortly before the stoat evolved as its mirror image in Eurasia. The species thrived during the Ice Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. The long-tailed weasel and the stoat remained separated until half a million years ago, when falling sea levels exposed the Bering land bridge, thus allowing the stoat to cross into North America. However, unlike the latter species, the long-tailed weasel never crossed the land bridge, and did not spread into Eurasia.[2]

Physical description

The long-tailed weasel is one of the largest members of the genus Mustela in North America, with a total length of 300"?350 mm and a tail comprising 40"?70% of the head and body length. In most populations, females are 10"?15% smaller than males,[3] thus making them about the same size as large male stoats.[4] The eyes are black in daylight, but glow bright emerald green when caught in a spotlight at night.[5] The dorsal fur is brown in summer, while the underparts are whitish and tinged with yellowish or buffy brown from the chin to the inguinal region. The tail has a distinct black tip. Long-tailed weasels in Florida and the southwestern US may have facial markings of a white or yellowish colour. In northern areas in winter, the long-tailed weasel's fur becomes white, sometimes with yellow tints, but the tail retains its black tip.[3] The long-tailed weasel moults twice annually, once in autumn (October to mid-November) and once in spring (March"?April). Each moult takes about 3"?4 weeks and is governed by day length and mediated by the pituitary gland. Unlike the stoat, whose soles are thickly furred all year, the long-tailed weasel's soles are naked in summer.[4] The long-tailed weasel has well-developed anal scent glands, which produce a strong and musky odour. Unlike skunks, which spray their musk, the long-tailed weasel drags and rubs its body over surfaces in order to leave the scent.[6]

Behavior Reproduction and development

The long-tailed weasel mates in July"?August, with implantation of the fertilized egg on the uterine wall being delayed until about March. The gestation period lasts 10 months, with actual embryonic development taking place only during the last four weeks of this period, an adaptation to timing births for spring, when small mammalsare abundant. Litter size generally consists of 5"?8 kits, which are born in April"?May. The kits are born partially naked, blind and weighing 3 grams, about the same weight of a hummingbird. The long-tailed weasel's growth rate is rapid, as by the age of three weeks, the kits are well furred, can crawl outside the nest and eat meat. At this time, the kits weigh 21"?27 grams. At five weeks of age, the kit's eyes open, and they become physically active and vocal. Weaning begins at this stage, with the kits emerging from the nest and accompanying the mother in hunting trips a week later. The kits are fully grown by autumn and, by this time, the family disbands. The females are able to breed at 3"?4 months of age, while males become sexually mature at 15"?18 months.[6]

Denning and sheltering behaviour

The long-tailed weasel dens in ground burrows, under stumps or beneath rock piles. It usually does not dig its own burrows, but commonly uses abandoned chipmunk holes. The 22"?30 cm diameter nest chamber is situated around 60 cm from the burrow entrance, and is lined with straw and the fur of prey.[6]

Diet

The long-tailed weasel is a fearless and aggressive hunter which may attack animals far larger than itself. When stalking, it waves its head from side to side in order to pick up the scent of its prey. It hunts small prey, such as mice, by rushing at them and kills them with one bite to the head. With large prey, such as rabbits, the long-tailed weasel strikes quickly, taking its prey off guard. It grabs the nearest part of the animal and climbs upon its body, maintaining its hold with its feet. The long-tailed weasel then manoevres itself to inflict a lethal bite to the neck.[7]

The long-tailed weasel is an obligate carnivore which prefers its prey to be fresh or alive, eating only the carrion stored within its burrows. Rodents are almost exclusively taken when they are available. Its primary prey consists of mice, rats, squirrels, chipmunks, shrews, moles and rabbits. Occasionally, it may eat small birds, bird eggs, reptiles, amphibians, fish, earthworms and some insects. The species has also been observed to take bats from nursery colonies. It occasionally surplus kills, usually in spring when the kits are being fed, and again in autumn. Some of the surplus kills may be cached, but are usually left uneaten. Kits in captivity eat from ¼"?½ of their body weight in 24 hours, while adults eat only one fifth to one third. After killing its prey, the long-tailed weasel laps up the blood, but does not suck it, as is popularly believed. With small prey, also the fur, feathers, flesh and bones are consumed, but only some flesh is eaten from large prey. When stealing eggs, the long-tailed weasel removes each egg from its nest one at a time, then carries it in its mouth to a safe location where it bites off the top and licks out the contents.[7]

Subspecies

As of 2005[update],[8] 42 subspecies are recognised.

Subspecies Trinomial authority Description Range Synonyms Bridled weasel
Mustela f. frenata

(Nominate subspecies)

Lichtenstein, 1831 A large subspecies with a long tail, relatively short black tip and has a black head with conspicuous white markings[9] Mexico aequatorialis (Coues, 1877)

brasiliensis (Sevastianoff, 1813)
mexicanus (Coues, 1877)

Mustela f. affinis Gray, 1874 A large, very dark subspecies with very little white marking on the face[10] costaricensis (J. A. Allen, 1916)

macrurus (J. A. Allen, 1912)
meridana (Hollister, 1914)

Mustela f. agilis Tschudi, 1844 macrura (J. A. Allen 1916) Black Hills weasel
Mustela f. alleni Merriam, 1896 Similair to arizonensis in size and general characters, but with yellower upper parts[11] Black Hills, South Dakota Mustela f. altifrontalis Hall, 1936 saturata (Miller, 1912) Arizona weasel
Mustela f. arizonensis Mearns, 1891 Similair to longicauda, but smaller in size[12] Sierra Nevada and Rocky Mountain systems, reaching British Columbia in the Rocky Mountain region Mustela f. arthuri Hall, 1927 Mustela e. celenda Hall, 1944 Mustela f. aureoventris Gray, 1864 affinis (Lönnberg, 1913)

jelskii (Taczanowski, 1881)
macrura (Taczanowski, 1874)

Mustela f. boliviensis Hall, 1938 Mustela f. costaricensis Goldman, 1912 brasiliensis (Gray, 1874) Mustela f. effera Hall, 1936 Chiapas weasel
Mustela f. goldmani Merriam, 1896 Similair to frenata in size and general characters, but with a longer tail and hind feet, darker fur and more restricted white markings[13] Mountains of southeastern Chiapas Mustela f. gracilis Brown, 1908 Mustela f. helleri Hall, 1935 Mustela f. inyoensis Hall, 1936 Mustela f. latirostra Hall, 1896 arizonensis (Grinnell and Swarth, 1913) Mustela f. leucoparia Merriam, 1896 Similair to frenata, but slightly larger and with more extensive white markings[14] Common long-tailed weasel
Mustela f. longicauda

Bonaparte, 1838 A large subspecies with a very long tail and short black tip. The upper parts are pale yellowish brown or pale raw amber brown, while the underparts vary in colour from strong buffy yellow to ochraceous orange[15] Great Plains from Kansas northward Mustela f. macrophonius Elliot, 1905 Mustela f. munda Bangs, 1899 Mustela f. neomexicanus Barber and Cockerell, 1898 Mustela f. nevadensis Hall, 1936 longicauda (Coues, 1891)
Mustela f. nicaraguae J. A. Allen, 1916 Mustela f. nigriauris Hall, 1936 xanthogenys (Gray, 1874)

Mustela f. notius

Bangs, 1899 New York weasel
Mustela f. noveboracensis

Emmons, 1840 A large subspecies, with a shorter tail than longicauda. The upper parts are rich, dark chocolate brown, while the underparts and upper lip are white and washed with yellowish.[16] Eastern United States from southern Maine to North Carolina and west to Illinois fusca (DeKay, 1842)

richardsonii (Baird, 1858)

Mustela f. occisor Bangs, 1899 Mustela f. olivacea Howell, 1913 Oregon weasel
Mustela f. oregonensis Merriam, 1896 Similair to xanthogenys, but larger, darker in colour and has more restricted facial markings[17] Rogue River Valley, Oregon Mustela f. oribasus Bangs, 1899 Mustela f. panamensis Hall, 1932 Florida weasel
Mustela f. peninsulae

Rhoads, 1894 Equal in size to noveboracensis, but with a skull more similair to that of longicauda. The upper parts are dull chocolate brown, while the underparts are yellowish[18] Florida Peninsula Mustela f. perda Merriam, 1902 Mustela f. perotae Hall, 1936 Mustela f. primulina Jackson, 1913 Mustela f. pulchra Hall, 1936 Cascade Mountain weasel
Mustela f. saturata Merriam, 1896 Similair to arizonensis, but larger and darker, with an ochraceous belly and distinct spots behind the corners of the mouth[19] Mustela f. spadix Bangs, 1896 Similair to longicauda, but much darker[20] Mustela f. texensis Hall, 1936 Tropical weasel
Mustela f. tropicalis

Merriam, 1896 Similair to frenata, but much smaller and darker, with less extensive white facial marking and an orange underbelly[21] Tropical coast belt of southern Mexico and Guatemala from Vera Cruz southward frenatus (Coues, 1877)

noveboracensis (DeKay, 1840)
perdus (Merriam, 1902)
richardsoni (Bonaparte, 1838)

Washington weasel
Mustela f. washingtoni Merriam, 1896 Similair to noveboracensis in size, but with a longer tail and shorter black tip[22] Washington state California weasel
Mustela f. xanthogenys Gray, 1843 A medium sized subspecies with a long tail, a face marked with whitish and ochraceous underparts[17] Sonoran and Transition faunas of California, on both sides of Sierra Nevada